Dish washing machines used in restaurants, institutions and other commercial facilities which wash dishes in high volume are available in a variety of different types. One type that is advantageous in many applications is an under counter unit that is installed beneath a counter top. This type of dishwasher has size constraints because of the need to install it under a standard counter top (usually only 34 inches high). As a result, it is important to keep the size of the wash compartment as large as possible in order to avoid unduly limiting the capacity of the machine.
One problem is that the machine must normally be equipped with upper and lower spray arms that necessarily occupy space in the wash compartment. Typically, the upper spray arm is mounted at the top of the cabinet with a spray base that supplies water to it located as high as possible. Because the spray arm is located below the spray base, the spray arm extends downwardly a considerable distance below the top of the wash compartment. Thus, a fairly large amount of essentially wasted space is located at the top of the cabinet above the spray arm. The pumps and controls are usually housed in the bottom of the cabinet below the wash compartment floor. Accordingly, the space required for these components determines the height of the wash compartment floor and thus the height of the lower spray arm.
Dish washing machines of this type are often constructed for operation as batch units. Water collected in the basin or sump of the machine is pumped to the spray arms during a wash cycle, after which the wash water is drained and incoming water is added and pumped to the spray arms for a rinse cycle using clean water. The next machine cycle uses the leftover rinse water for the wash water.
A major problem with this type of batch operated machine is that some of the soiled water does not drain out and is applied with the new rinse water during the rinse cycle. Consequently, the rinse water is partially soiled and the effectiveness of the dish washing suffers. Although measures have been taken to reduce the harmful effects of the leftover water, they have not been entirely successful and have at best achieved inconsistent results.
In order to keep food scraps and other materials from clogging the pump and the spray arms, a pump filter is normally installed in the sump area. While the filter can prevent clogging of the pump and spray arms, food materials become lodged in the pump filter so that the rinse water is drawn through matted soil in the filter and is mixed with the leftover wash water. Clogging of the filter also reduces the flow area available for water to flow to the pump, and operating pressure is lost. In order to minimize this problem, the filter must be removed and cleaned at frequent intervals. At best, this results in significant maintenance requirements and at worst, the filter is not adequately cleaned and the machine is ineffective.
Large items such as broken glass, straws, toothpicks and the like do not affect the quality of the rinse water. Thus, scrap accumulators in the flow path can be provided to collect these types of materials without adverse affects on the machine operation. In an under counter machine, the provision of a scrap accumulator presents unique difficulties. If the accumulator is outside of the sump and cannot be pumped reliably, there is a risk of flooding that may not be detected early enough to avoid serious damage because of the location of the machine beneath the counter. A "closed" accumulator outside of the sump occupies space that could otherwise be used as part of the wash compartment. A gravity flow system with a sealed accumulator reduces the wash compartment size to an even greater extent.
The dishwasher receives water through a flexible hose which normally connects with the building water supply. Typically, the hose is constantly filled with water and is thus continually subjected to water pressure. This constant pressure can result in a hose rupture which can cause serious and costly flooding, especially if it occurs when the building is unoccupied and there is no one to notice and attend to the flooding problem.